Neurostimulation is the application of electrical stimulation on neurological pathways, such as nerve bundles, neurovascular bundles, and so forth. Electrical stimulation has a history in medicine for treating various ailments. For example, neurostimulation has been used for the treatment of chronic radiculopathy (sciatica), failed back syndrome, neuropathy, reflex sympathetic dystrophy (complex regional pain syndrome), and various vascular insufficiencies.
In addition, vagus nerve stimulation (VNS) has been applied with partial success in patients with refractory epilepsy. In this procedure, an implantable pulse generator is implanted in the patient's thorax, and an electrode lead is routed from the generator to the left vagus nerve in the neck. Helix-shaped stimulation and indifferent electrode contacts are attached to the vagus nerve via an invasive surgical process that requires the carotid sheath to be fully exposed. Based on a number of studies, approximately 5% of patients undergoing VNS are seizure-free, and an additional 30-40% of patients have a greater than 50% reduction in seizure frequency. However, VNS may lead to significant side effects. The vagus nerve provides parasympathetic innervation to the cardiac tissue, and thus VNS may lead to bradycardia, arrhythmia, or even graver cardiac side effects. In fact, VNS systems are often only used on the left vagus nerve, as the right vagus nerve contributes significantly to cardiac innervation. Additionally, VNS may interfere with proper opening of the vocal cords, which has led to hoarseness and shortness of breath in a significant number of VNS patients.
Electrical stimulation has also been used to treat erectile dysfunction. The targets of electrical stimulation are the cavernous nerves. The cavernous nerves run bilaterally between the prostate and the rectum as they course from the sacral spinal cord to the corpora cavernosa in the penis. Near the rectum the nerves form more of a plexus than a coherent nerve, and they are interlaced with small arteries and veins as well as fatty tissue. This collection of small nerve fibers, arteries, and veins can be referred to as the neurovascular bundle.